[RFC PATCH v5 12/19] virtio/vsock: fetch length for SEQPACKET record

[Arseny Krasnov <arseny.krasnov@xxxxxxxxxxxxx>]

This adds transport callback which tries to fetch record begin marker
from socket's rx queue. It is called from af_vsock.c before reading data
packets of record.

Signed-off-by: Arseny Krasnov <arseny.krasnov@xxxxxxxxxxxxx>
---
 include/linux/virtio_vsock.h            |  1 +
 net/vmw_vsock/virtio_transport_common.c | 53 +++++++++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index 003d06ae4a85..022667d57884 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -85,6 +85,7 @@ virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
 			       struct msghdr *msg,
 			       size_t len, int flags);
 
+size_t virtio_transport_seqpacket_seq_get_len(struct vsock_sock *vsk);
 int
 virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
 				   struct msghdr *msg,
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index d8ec2dfa2315..e9a2de72ebbf 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -399,6 +399,59 @@ static inline void virtio_transport_remove_pkt(struct virtio_vsock_pkt *pkt)
 	virtio_transport_free_pkt(pkt);
 }
 
+static size_t virtio_transport_drop_until_seq_begin(struct virtio_vsock_sock *vvs)
+{
+	struct virtio_vsock_pkt *pkt, *n;
+	size_t bytes_dropped = 0;
+
+	list_for_each_entry_safe(pkt, n, &vvs->rx_queue, list) {
+		if (le16_to_cpu(pkt->hdr.op) == VIRTIO_VSOCK_OP_SEQ_BEGIN)
+			break;
+
+		bytes_dropped += le32_to_cpu(pkt->hdr.len);
+		virtio_transport_dec_rx_pkt(vvs, pkt);
+		virtio_transport_remove_pkt(pkt);
+	}
+
+	return bytes_dropped;
+}
+
+size_t virtio_transport_seqpacket_seq_get_len(struct vsock_sock *vsk)
+{
+	struct virtio_vsock_seq_hdr *seq_hdr;
+	struct virtio_vsock_sock *vvs;
+	struct virtio_vsock_pkt *pkt;
+	size_t bytes_dropped;
+
+	vvs = vsk->trans;
+
+	spin_lock_bh(&vvs->rx_lock);
+
+	/* Fetch all orphaned 'RW' packets and send credit update. */
+	bytes_dropped = virtio_transport_drop_until_seq_begin(vvs);
+
+	if (list_empty(&vvs->rx_queue))
+		goto out;
+
+	pkt = list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, list);
+
+	vvs->user_read_copied = 0;
+
+	seq_hdr = (struct virtio_vsock_seq_hdr *)pkt->buf;
+	vvs->user_read_seq_len = le32_to_cpu(seq_hdr->msg_len);
+	vvs->curr_rx_msg_cnt = le32_to_cpu(seq_hdr->msg_cnt);
+	virtio_transport_dec_rx_pkt(vvs, pkt);
+	virtio_transport_remove_pkt(pkt);
+out:
+	spin_unlock_bh(&vvs->rx_lock);
+
+	if (bytes_dropped)
+		virtio_transport_send_credit_update(vsk);
+
+	return vvs->user_read_seq_len;
+}
+EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_seq_get_len);
+
 static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
 						 struct msghdr *msg,
 						 bool *msg_ready)
-- 
2.25.1